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TPD4S014DSQR - ACK rebound after about 1 second

sebastien72887
Prodigy 100 points

We are using the TPD4S014DSQR for USB protection (voltage and ESD).

 

On some boards (1/2), we have an abnormal comportement of the ACK pin (pin 4).

When USB power is disconnected, the nACK is driven high by the pull-up.

But the problem is after about 1 second the TPD4S014DSQR nACK is driven low for 250mS.

 

We have disconnected the MCU input on the nACK net.

 

CH1: USB_POWER

CH2: P5V_USB

CH3: nACK

CH4: P2V_TO_P3V3

 

Thank you for your kind reply,

  • 0
    TI__Expert 3500 points
    Sebastian-

    I'm working to get an answer to your question and will get back to you when I get an answer within the next few days. Thank you for your patience.

    Thanks,
    Alec
  • 0 in reply to Alec Forbes
    TI__Expert 3500 points
    Sebastian-

    Looking at this, its not immediately obvious what would be causing this behavior on the ACK pin.

    Is it correct that on your 2 boards, this occurs on only one of them? If that is case, are there any differences in the two boards schematic or layout that could possibly explain this?

    Are there any temperature overheating issues on this board? If the device goes into thermal protection mode, it asserts the ACK pin even in UVLO. Could you also check to make sure that there is no bounce on the EN pin of the device?

    Thanks for your patience, if you'll provide me with this information I can help diagnose this issue for you.
    Alec
  • 0 in reply to Alec Forbes
    Prodigy 100 points

    Alec,

    1/

    We have made 50 boards (first product) and the problem is on half of them. All boards are identical.

    A board where the problem is detected, the problem systematically appears.

    2/

    The problem systematically appears board cold or not. I have not paste the EN signal but it is completly stable to 0V.

    Problem: The bad bounce on the ACK (ACK driven to 0V) signals a correct input voltage. So it is not a temperature overheating detection.

    Datasheet:

    Open-Drain Adapter-Voltage Indicator Output. ACK is driven low after the VIN voltage is stable
    ACK 4 I between UVLO and OVLO for 17 ms (typ). Connect a pullup resistor from ACK to the logic I/O
    voltage of the host system.

    Thank you for your help,

    Sebastien

  • 0 in reply to sebastien72887
    TI__Expert 3500 points
    Sebastien-

    It's very strange that half your boards have this issue and half do not have the issue. I'm discussing this with our design team to see if there is an explanation for this behavior, and will report back once I have more information.

    Thanks,
    Alec